THE BACTERIOPHAGE CORPUSCLE 91 



//. Agar plates held at 30°C. 



Suspension 1 . . . Sterile 



Suspension 2. . .Traces of growth 



Suspension 3. . .Fragments of growth 



Suspension 4. . .About 50 plaques, having a diameter of about 7 mm. 



III. Agar plates held at 18°C. 



Suspension 1 . . . Sterile 



Suspension 2. . .Sterile 



Suspension 3. . .Scattered traces of growth 



Suspension 4. . .Confluent plaques (about 50), with a diameter of about 13 



IV. Gelatin plates held at 18°C. 



Suspension 1 . . . Continuous bacterial layer, absolutely like a normal culture 

 Suspension 2. . .Continuous bacterial layer 

 Suspension 3. . .Continuous bacterial layer 

 Suspension 4. . .Continuous bacterial layer 



V. Gelatin plates with a substratum of agar 



Suspension 1 . . . Sterile 



Suspension 2. . .Sterile 



Suspension 3. . .Culture debris 



Suspension 4. . .About 50 plaques, with diameters of 3 to 4 mm. 



This experiment, repeated upon three different occasions, has ahvays 

 given similar results. By varying the depth of the gelatin layer I have 

 observed that the size of the plaques varies inversely with the depth of 

 the layer. When the layer was about 3 mm. in depth the bacterial 

 culture appeared normal. 



Obviously it is not the gelatin as such which interferes with the 

 process of bacteriophagy. It is simply because the gelatin is but 

 slightly permeable to the products arising in the course of the phenom- 

 enon that an inhibitory effect is manifested. When the layer is 

 very thin and is superimposed upon a permeable substratum bacteri- 

 ophagy occurs just as it does on agar. 



The experiment also shows some points with regard to the effect of 

 temperature. 



The dimensions of the plaque resulting, one might say, from a ''race" 

 between the rate of multiplication of the bacterium and that of the 

 bacteriophage, it follows that at a given temperature the one or the 

 other may be ''handicapped." On the other hand, experiment definitely 



